The invention relates to a process for control of boost pressure of a turbocharger in an internal combustion engine as a function of the density of ambient air, an internal combustion engine with exhaust gas turbocharger and with control means for control of the boost pressure in which the actual boost pressure is determined at specific time intervals and compared with assigned values for the desired boost pressure taken from stored compressor characteristics and readjusted, and with an engine control device for an internal combustion engine with exhaust gas turbocharger having a control unit for control of the boost pressure and a data storage unit.
Control of the boost pressure of an internal combustion engine with a turbocharger is of the state of the art. For example, DE 197 57 661 C1 discloses boost pressure control in an internal combustion engine with turbocharger in which a desired boost pressure is determined from characteristics determined by engine speed and load and is taken into account for control of unstable influences based on dynamic road behavior.
As soon as the supercharger speed exceeds a maximum permissible boundary value for the supercharger speed, a turbocharger can be damaged. Such excessive speed may come about if the vehicle is in operation at higher altitudes in which the ambient pressure falls below a specific minimum pressure or the absorption line of the engine changes radically as a result of leaks from the system. In order to prevent overspeed of the turbocharger in operation at a high altitude, the speed of the turbocharger is usually restricted by limiting the boost pressure as a function of the engine speed and atmospheric pressure. This is accomplished by means of previously recorded characteristics in which the boost pressure is filed on the basis of ambient pressure and engine speed. For this purpose costly tests for determining the characteristics must be carried out in advance for each altitude for every engine having a turbocharger. In addition, fluctuations in air pressure and in ambient temperature must be predicted in the design process.
The object of the invention is to limit overspeed of the turbocharger in an internal combustion engine having a turbocharger by a simple and reliable process in which allowance is made for atmospheric conditions despite high performance.
It is claimed for the invention that this object is attained both by the process for control of boost pressure limitation of a turbocharger in an internal combustion engine as a function of the density of ambient air in accordance with the characteristics specified in claim 1 and by designing an internal combustion engine having a exhaust gas turbocharger and by means for control of the boost pressure in which the actual boost pressure is determined at specific time intervals and compared with assigned values for the desired boost pressure in a particular operational condition determined from stored compressor characteristics and reset, in accordance with the characteristics specified in claim 9, and by means of an engine control device for an internal combustion engine with exhaust gas turbocharger having a control unit for adjustment of the boost pressure and a data storage unit in accordance with the characteristics specified in claim 10.
As a result, the boost pressure as a function of atmospheric conditions is determined simply at each determination point, with the atmospheric conditions taken into account, and this boost pressure is compared with the maximum boost pressure permissible for this operating condition. Without costly pretesting for determination of a set of characteristics for each individual ambient situation the measured boost pressure may be compared directly with the maximum permissible boost pressure taken from a set of characteristics to determine if the compressor speed is still below the boundary with overspeed and accordingly to prevent further increase when the boundary state is reached.
By preference the process as specified in claim 2, in which the adjusted air mass throughput at the compressor intake may be determined with very good approximation, is to be carried out.
The process as specified in claim 3 permits control and boost pressure limitation in a simple manner by means of the engine control means usually already present as part of the structure, means in which all predetermined data are present and to which all measured data are first delivered through corresponding inputs and from which corresponding control signals for boost pressure control may be forwarded by way of an output.
The process as specified in claim 4 permits especially precise determination of the pressure relationships PLPVE by taking into account the pressure losses between measuring point and compressor intake. This makes it possible further to minimize the confidence interval between maximum permissible compressor speed and compressor speed as measured. The performance spectrum of the engine may in this way be extended directly to higher levels.
Preference is to be given to the process as specified in claim 5, a process by which it is possible additionally to minimize the danger of short-term occurrence of boost pressure peaks situated above the maximum permissible boost pressure and accordingly the occurrence of short-term compressor speed peaks situated above the maximum permissible value for the compressor speed on the basis of dynamic processes. Overspeed of the compressor as a result of dynamic processes and the speed peaks caused by them can thus be prevented by simple means.
Claims 6 to 8 represent especially advantageous processes for control of boost pressure limitation.